Distinguish between internal and extarnal commands with examples for unix?

Answer 1

Internal commands are executed by the shell and do not exist as a separate binary program. You can find out which of these there are by looking at the 'man' entry for the shell you are using.

External commands can be found in various directories, such as /bin, /usr/bin, etc.

Answer 2

It depends on the shell program you are running in your environment; there are a number of 'internal' commands that are recognized by the shell and do not exist as "commands" on the system anywhere.

Any command that is not internal to the shell would be considered an external command. To find a list of basic external commands, try to do a 'ls /bin', which lists very essential and common external Unix commands.

Look at the 'man' or 'info' entry for your shell to find a list of internal commands.

An internal command would be one that is recognized by the shell and the shell does not have to execute a program to do the command. An example would be the 'alias' command, which creates, removes, or lists aliases in the environment.

An external command would be one that you might find in the /bin directory, such as 'ls'.

Answer 3

Internal commands are executed by the shell itself; it does not need to go outside the program to find and load a program. You can find the internal commands for any shell by looking at the 'man' page for that shell.

Anything not directly interpreted by the shell is an external command, and would have to be found by looking at the $PATH variable of the shell.

For example, 'set' or 'alias' are typically internal commands, whereas commands such as 'ls', 'grep', 'find' are examples of external commands. You can find external commands as filenames in various directories.